Etching of openings for forming electrical interconnects in the semiconductor processing industry is becoming more demanding as device sizes shrink. For example, as device sizes shrink to 0.15 microns and below, the location and etching profiles of electrical contact holes is increasingly important to avoid overetching and misalignment which can cause electrical shorting thereby reducing device yield as well as reliability.
Undesired step heights produced by conformal or blanket deposition of dielectric insulating layers is particularly an issue in depositing pre-metal dielectric (PMD) layers over semiconductor devices formed on a semiconductor substrate. For example, planarization of the PMD layer is important to accurately and reliably form contacts to electrically connect the device to subsequently formed overlying levels of wiring. For example, step heights or topography variations of the PMD layer following deposition can be as high as 1 micron or more. Consequently, chemical mechanical polish (CMP) processes are not favored for planarization due to the large amount of material which must be removed by CMP to achieve a desired degree of planarization, thereby increasing processing cost.
Prior art approaches have proposed used dry etchback processes in PMD planarization processes. While this approach is generally effective for small variations in topography, etchback approaches for larger variations in topography (step heights) may not be adequately planarized the PMD layer, due to preferential or overetching during the etchback process leading to depressed areas which create problems in subsequent formation of contact holes including backfilling with metal.
There is therefore a continuing need in the integrated circuit manufacturing art for improved and cost effective planarization methods to increase device yield and reliability.
It is therefore an object of the invention to provide an improved and cost effective planarization method to increase device yield and reliability, as well as overcoming other shortcomings in the prior art.